In known manner, a propulsion system of an aircraft includes a nacelle in which an engine is disposed substantially concentrically. The nacelle includes at the front an air intake that is extended inside the nacelle by a duct for channeling the air in the direction of the engine.
Under some conditions, frost or ice may tend to form at the level of the air intake. It is necessary to limit this formation of frost or ice in order to prevent blocks of ice being ingested by the engine and damaging it. To this end, the nacelle includes a de-icing (Nacelle Anti Ice) device. In the remainder of the description, the term de-icing encompasses the treatment of both frost and ice.
The present invention relates more particularly to nacelles incorporating a pneumatic de-icing device utilizing hot air bled from the compressor of the engine and injected at the level of the air intake and more particularly brought into contact with the internal wall of the air intake.
In an embodiment known from the documents FR-2.813.581 and U.S. Pat. No. 6,443,395, shown in FIG. 1, a nacelle includes internally a partition 12 referred to as the “front frame” that delimits with the air intake 14 an annular duct 16 also known as the “D-duct” that extends all around the circumference of the nacelle and has an approximately D-shaped section.
This duct 16 includes a hot air feed with at least one orifice 18 and an exhaust 20 for evacuating the cooled air used for de-icing.
The hot air is bled at the level of an outlet 24 of a compressor stage of the engine 22 and the hot air feed includes a pipe 26 for routing it to the orifice 18. This pipe 26 includes means 28 for measuring the pressure and a device for regulating the pressure in order to deliver the required quantity of hot air to the orifice 18.
An engine 22 includes a plurality of outlets 24, 24′, 24″ each with a different temperature/pressure combination. The outlet 24 is chosen by arriving at a compromise between the hot air requirements for de-icing and the structural and thermal capabilities of the air intake 14. Thus the bled flow of air must have a high pressure and a high temperature to ensure effective de-icing. On the other hand, too high a temperature and/or pressure may damage the air intake, which is generally made from composite materials and/or aluminum alloy.
The device for regulating the pressure includes a first pressure regulator valve 30 and a pressure regulator and shut-off valve 32.
The pressure regulator valve 30 is controlled by a solenoid and can occupy two positions as a function of a signal S1 received by the solenoid, a totally open position when receiving a signal S1 and a regulated position in the absence of a signal S1. This valve 30 is regulated pneumatically with a single regulation level.
The pressure regulator and shut-off valve 32 is controlled by two solenoids adapted to receive respective signals S2 and S3. Accordingly, the pressure regulator and shut-off valve 32 can occupy three positions, a fully open position in the absence of signals S2 and S3, a regulated position on reception of a signal S2 and a closed position on reception of a signal S3. This valve 32 is regulated pneumatically with a single regulation level identical to that of the pressure regulator valve 30.
In the absence of electrical signals S1, S2, S3, the pressure regulator and shut-off valve 32 is in the fully open position while the regulator valve 30 is in the regulated position.
In a known mode of operation, the valves 30 and 32 have the same regulation level with a set point pressure of the order of 5.175+/−0.3 bar (75+/−5 psig).
The valves 30 and 32 must have the same regulation level to provide a redundant regulation system, a malfunction of the pressure regulator valve 30 being compensated by the pressure regulator and shut-off valve 32 going to the regulated position on reception of a signal S2. Accordingly, the fully open position of each regulator valve is simply used to allow the other valve to perform the regulation according to the single regulation level and thus to prevent any pneumatic interaction between the two valves.
The de-icing device can occupy two states, an activated (ON) first state in which the air intake is fed with hot air at a pressure higher than the regulation level and a deactivated (OFF) second state in which the air intake is no longer fed with hot air.
Accordingly, in normal operation, the activated state corresponds to the regulated position of the pressure regulator valve 30 and to the fully open position of the pressure regulator and shut-off valve 32, in the absence of signals S1, S2, S3, or, in the event of a malfunction of the pressure regulator valve 30 in the fully open position, to the regulated position of the pressure regulator and shut-off valve 32, on reception of signal S2.
The deactivated state corresponds to the closed position of the pressure regulator and shut-off valve 32 on reception of a signal S3.
Even if it has numerous advantages, the prior art regulator device cannot be fully satisfactory because regulation can be effected only in accordance with a single regulation level.
Accordingly, in certain circumstances, for example for certain engines, it is not possible with a single regulation level to arrive at a compromise between effective de-icing and the maximum temperature and pressure acceptable by the air intake for all flight phases.
For other hot air requirements of the aircraft, such as air conditioning the cabin, for example, the flow of hot air bled from the engine must be regulated more flexibly, in accordance with a plurality of regulation levels.
To achieve this objective, a first solution consists in using at least two hot air outlets 24, 24′ of the engine, the two outlets being connected alternately as a function of the flight phases and/or external conditions. This solution is not entirely satisfactory because it leads to a more costly and more complex architecture that is not suitable for an engine environment that is already subject to severe constraints in terms of available space, temperature and vibration.
A second solution would be to use a heat exchanger to modify the temperature of the regulated flow of air. However, this solution is relatively costly and complex and leads to an increase in the onboard mass.
Finally, a third solution would be to use an electrohydraulic servovalve for proportional control of a hydraulic pressure (and therefore a degree of opening of the flap) as a function of an electrical signal. This solution is not entirely satisfactory because it leads to considerably increased complexity of the control logic, valve technology level and system control.